Navigation systems are available that provide users with various navigation-related functions. For example, some navigation systems are able to determine an optimum route to travel by roads between locations in a geographic region. Using input from the user, and optionally from equipment that can determine the user's physical location (such as a GPS system), a navigation system can examine various routes between two locations to determine an optimum route to travel from a starting location to a destination location in a geographic region.
To calculate an optimal route, the navigation system uses a routing algorithm. A routing algorithm searches for the route having the minimum cost. Here, cost refers to a user's preference for a route. For example, the user may desire the shortest route, the fastest route, or the most energy efficient route for traveling from an origin to a destination.
The routing algorithm uses data in a geographic database to calculate the route. The geographic database contains data that represents some of the physical geographic features in a geographic region. For example, the geographic database represents a road network using road segments and nodes. If the routing algorithm is calculating a minimum time route, the routing algorithm may retrieve road segment length and speed limit data from the geographic database. The cost per segment is the travel time, which is calculated by dividing the segment length by the speed limit associated with the segment.
To improve the minimum time route calculation, the routing algorithm may use traffic data. Some navigation systems have a database of historical traffic data, such as NAVTEQ's Traffic Patterns™ product. The historic traffic database includes data representing typical traffic speeds on roads organized by day of the week and time of the day. Route calculation using a historic traffic database is likely to be more accurate than calculating a route using speed limits or speed ranges to estimate the speed of traffic.
Route calculation using real-time traffic data is likely to be more accurate than calculating a route using a historic traffic database. In some areas, systems broadcast data messages that contain up-to-the-minute reports of traffic and road condition information. These systems broadcast the traffic data over traffic message channels on a continuous, periodic, or frequently occurring basis. Traffic message receivers decode the data and provide up-to-the-minute reports of traffic and road conditions.
One protocol for broadcasting traffic messages is the Traffic Message Channel (TMC), which is used in Europe, North America, and elsewhere. In Europe TMC is broadcast as part of the Radio Data System (RDS) and North America TMC is broadcast as part of the Radio Broadcast Data System (RBDS). Essentially RDS and RBDS are identical. Another traffic broadcast system, named Vehicle Information and Communication System (“VICS”) Center, is used in Japan. Traffic and road condition information can also be transmitted using other protocols (such as Traffic Experts Protocol Group (TPEG)) and on other broadcast bearers including Digital Audio Broadcasting (“DAB”), Digital Multimedia Broadcasting (“DMB”), Hybrid Digital Radio (“HD Radio”), Digital Radio Mondiale (DRM), satellite radio, and other protocols and radio systems, such as MSN-Direct.
Some systems may transmit real-time traffic data directly to an end-user device. For example, the system may use non-broadcast transmissions, such as General Packet Radio Service (GPRS), Time Division Multiplexing (TDM), or other direct wireless transmission.